How is it possible to know when a nickel-cadmium battery is fully charged?

• A. A simple voltage check during charging
• B. Temperature rise alone marks full charge
• C. Completely discharge, then charge with a constant current to 140% of its ampere-hour capacity
• D. Stop charging after a fixed time

Answer: (C)

Nickel-cadmium cells don’t give a reliable end-of-charge signal from voltage or temperature alone, because surface charge and varying conditions can mask the true state of charge. The dependable approach is to reset the battery by discharging it completely, then recharge with a constant current up to a defined energy input. Charging to 140% of the rated ampere-hour capacity after a full discharge ensures the cells have accepted more than their nominal capacity, reconditioning them and confirming a full charge. Stopping after a fixed time or relying only on voltage or temperature readings can mislead, since those indicators don’t guarantee all cells are properly replenished.